1. Field of the Invention
The present invention relates to a watch casing with a rotating bezel comprising an angular positioning device for the bezel, having a toothed rack and a spring-wire whose free end is resiliently and radially engaged in engagement with the toothed rack. The two parts in engagement, the spring and the toothed rack, are arranged to permit the displacement in angular steps of the bezel in both directions of rotation of the latter, the toothed rack and other end of the spring-wire being, the one integral with the rotating bezel, and the other with the casing.
2. Description of the Prior Art
In CH 536,509 there has already been proposed an angular positioning device for a rotating bezel, which requires equal forces to rotate the bezel in the two directions. To this end, an edgewise toothed rack is formed in a lower face of the rotating bezel, the teeth having a profile in the form of an equilateral or isosceles triangle. A piston is mounted in a cylindrical recess having a longitudinal axis parallel to the axis of rotation of the rotating bezel and formed in an upper face of the casing wall, immediately below the rotating bezel. This piston is pressed axially against the toothed rack of the rotating bezel by a spiral spring disposed between one end of the piston and the base of the cylindrical recess. The other end of the piston has a profile substantially matching the space between the two teeth. The angle formed by each face of the teeth relative to the longitudinal axis of the piston being the same, the force necessary to rotate the bezel is equal in the two directions of rotation.
The disadvantage of this solution lies in the large axial dimension occupied by the piston and spring device. If such a device can strictly speaking be fitted within the frame to work with an edgewise toothed rack to exert on it pressure parallel to the axis of rotation of the bezel, it is not usable due to lack of space with a toothed rack formed on a lateral face of the bezel on which the positioning device must apply a radial force. In effect, in this case the available space between the rotating bezel and the watch crystal which is located in the same plane in no case permits the piston positioning device to be accommodated, which must therefore work radially and no longer axially relative to the center of rotation of the rotating bezel.
EP-A-0 470 018 relates to a mechanism in which a spring in the form of an open ring has one end integral with a rotating leading element and another end resiliently engaged in a notch of a led rotating element, coaxial with the leading element. Above a given couple value, the leading and led rotating elements separate by sliding of the spring. Contrary to what is sought to be obtained by the present invention, one obtains by this mechanism a different sliding couple value according to the direction of rotation, as is specified in this document.
DE-A16 73 621 relates to a positioning mechanism for a toothed wheel comprising a spring fixed to a pin at one end and bearing on a second pin at the other end. The median portion of this spring situated at the apex of an obtuse angle between the two straight arms has a projecting portion in the form of an arc of a circle, which engages the teeth of the wheel. It is not a question, in this case, of a spring whose free end is in engagement with a toothed rack. It is in effect the median portion of the spring which serves to position the toothed rack. Given that one end of the spring is fixed while the other end can slide on the pin against which it abuts, the force necessary to overcome the pressure of the spring is not the same in the two directions of rotation of the wheel. In effect, in one direction the toothed rack exerts a force on the spring of which one component makes the free end of the spring slide against the pin, while in the opposite direction this same component is substantially parallel to the straight arm of the spring whose end is fixed to the other pin. As this end of the spring is fixed and the component of force is parallel to the straight arm of the spring, this component is neutralized and only the other component of force can bend the spring. This explains why this system does not permit one to work with the same force in the two directions of rotation of the positioning wheel and does not therefore offer a solution to the problem that one proposes to solve.
An object of the present invention is to overcome, at least in part,these disadvantages.